Pressed boards and wood composite materials are manufactured from mixtures of wood and one or more additives, such as adhesives and waxes. During manufacture, the wood-additive mixture is first laid down in batches on a conveyor belt in a loose mat, and this loose mat is then simultaneously compressed and heated. Heating the mat cures the binder and waxes present in the mixture wood-additive mixture as well as evaporates the moisture present in the raw materials, while by compressing the wood and additive materials are fused together to form a consolidated wood board.
Compression of the wood-additive may occur in a multi-platen press where several mat batches are set upon a series of press platens, and the batches compressed between adjoining platens. The platens are heated to high temperatures by passing a heating fluid through them and this heat in the platens is then dissipated as heat flows from the platens and into the mats while the mats are being compressed (the platens acting essentially as heat exchangers). As the platens dissipate or exchange heat into the wood mats, however, the temperature of the platens decreases, which is undesirable because at lower temperatures the binders and waxes in the wood-additive mixtures are slower to cure and thus require longer curing times. This temperature drop often occurs early in the pressing cycle, when the moisture content of the wood is highest, and is thus particular undesirable because wood is a poor conductor of heat, and high moisture concentrations are necessary to transfer heat into the interior of the wood-additive mat mixture.
Previously, in order to prevent this temperature loss during the pressing cycle, the press was maintained at a temperature higher than necessary so that as the temperature fell during compression, the temperature remained sufficiently high to promote the curing of the binder and the production of a solid wood composite product. The temperature of the platens is regulated and monitored by measuring the temperature of the oil that is supplied to the press at the inlet.
While this over-compensation technique may prevent the deleterious temperature drop that could impair the curing rate, it also has disadvantages. In particular, maintaining the press platens at these high temperatures has been noted to increase the incidence of press fires, particularly after long periods of downtime. Moreover, because the temperature cannot be accurately controlled, the press cycle is lengthened so as to ensure that sufficient heat is transferred to the batches of the wood-additive mixture to complete the curing and fusing processes. Furthermore, this over compensation technique is not an efficient use of energy.
Given the foregoing there is a continuing need for an apparatus and method for producing pressed boards and composite wood products whereby the temperature of the press platens can be effectively regulated so that the press cycle length is shortened, the possibility of press fires minimized, and the press operated under energy-efficient conditions.